1. Field of the Invention
The present invention concerns a method of sensing and indicating errors in a dosing circuit, in which a pumping device pumps a fluid via a conduit system out to at least one dosing device located nearby a dosing place. This dosing device measures and discharges intermittently a pre-determined volume of the fluid through a non-return valve out to the dosing place, when the pressure in the conduit system is increased from a low pressure to a high pressure during a certain limited time. A dosing device of this kind comprises an inlet and an outlet for the fluid, a charging chamber connected to said inlet, a dosing chamber connected to said outlet, a closable passage connecting the chambers and a movable body, which on one of its sides is subjected to the pressure in the charging chamber and on its opposite side is subjected to the pressure in the dosing chamber. Upon increase of the pressure in the conduit system to said high pressure the movable body moves in a way such that the volume of the dosing chamber decreases and the volume of the charging chamber increases, during which movement the passage between the chambers is closed, whereby fluid is discharged out of the dosing chamber through said outlet and non-return valve to the relevant dosing place and fluid is flowing into the charging chamber from the conduit system. Upon decrease of the pressure in the conduit system to said low pressure, the movable body moves in the opposite direction by the force of a resetting device, thereby pressing the fluid located in the charging chamber through said passage to the dosing chamber. A valve is arranged to prevent outflow through the inlet.
2. Description of Related Art
Dosing circuits of this kind exist in many applications. Often the dosing is of crucial importance for a process or a machine to operate in a satisfactory manner. Therefore, these dosing circuits usually are provided with equipment for sensing of errors in the dosing circuit.
Common to hitherto known equipment for sensing of errors in dosing circuits is that it does not give a reliable sensing of errors for all types of errors, which can occur in the circuit. Usually, the condition in the dosing circuit is sensed via a parameter, which is not representative for the condition at the very dosing place but for the condition in the central parts of the dosing circuit.
One example of an application, in which a reliable sensing of errors in the dosing circuit is of great importance, is lubrication of various machine elements such as bearings. The endurance of a bearing is reduced considerably if lubrication of it can not keep the friction and the heat generation caused thereby at a low level.
In hitherto known lubrication devices checking that lubrication is performed satisfactorily is made by inspection through sight glasses, by measuring of the lubricant level in a lubricant tank or by measuring of the pressure in a closed or open lubricant circuit, which continuously or intermittently provides the machine element with a lubricant by spraying or dosing of a predetermined volume of the lubricant.
In the Swedish patent publication 7214186-4 (publication No. 371 878) there is shown a distribution plant for lubricant, in which an error is indicated by a leakage flow, which directly or indirectly is caused by the error. In the known equipment the total flow of the lubricant in a main conduit is distributed out through a number of branch conduits. Each one of these provides a lubrication place with lubricant via two flow regulating inserts connected in series. An error in the lubricant circuit causes changes in the flow through the inserts, which in turn causes the pressure in a conduit between the inserts to vary. When the pressure in said conduit differs from a predetermined interval, a valve is opened to let out of the main conduit the leakage flow indicating the error.
The supply of lubricant to a bearing is often dimensioned in a way such that the lubricant also can carry away the heat generated in or transferred to the bearing by heat conduction. However, if a bearing is charged with more lubricant than is needed to maintain an oil film having enough carrying capacity, the friction losses and, thus, the heat generation in the bearing will increase. At high rotational speeds in bearings it is thus desirable to keep the supply of lubricant at a level as low as possible without risking the carrying capacity of the oil film. However, this means a reduced margin in the supply of lubricant, which in turn results in increasing risks and consequently higher demands on a rapid and reliable sensing of all errors crucial for the maintenance of the lubrication function.
Bearings in high speed rotating machines, such as centrifugal separators, often need a very small flow of lubricant, whereby they become sensitive to variation in the flow of lubricant. Therefore, clogging of a channel for the lubricant or admixture of air in the lubricant means great risks for the operation of these machines.